The present invention relates to medical devices, and more particularly to a new method for inducing vibrations in such devices while they are disposed within a living body.
Vibrating medical devices, such as intravascular devices used in intravascular intervention, have been known in the art for some time and have been employed for a variety of uses. Such uses include, for example, facilitating the advancement of a catheter or guidewire through the vasculature to a target site by reducing the vessel wall friction encountered by the device, and breaking up thrombi and other intravascularly disposed masses either through direct mechanical contact, generation of ultrasound or pressure weaves to impact the mass, or enhancing the action of lysing agents.
One such prior art device is described in U.S. Pat. No. 5,243,997 to Uflacker et al., which discloses a vibrating device for a guidewire that consists of an electric motor mounted within a case and a clamp member mounted to the eccentric output shaft of the motor for securing and vibrating the guidewire. A physician can use this device for facilitating the introduction and advancement of a guidewire through a patient's vasculature. Alliger et al, in their U.S. Pat. No. 4,920,954 disclose a device for applying cavitation forces to a mass such as artery plaque through a guidewire vibrated by a transducer disposed within a handpiece that also supports the guidewire. The patent also discloses certain preferred modulus of elasticity and diameters for the guidewire.
U.S. Pat. No. 5,626,593 to Imran discloses a catheter with a solenoid disposed at its tip to vibrate a rounded tip and thus allow the catheter to more easily cross stenoses or lesions occluding a patient's vessel. The solenoid is supplied with current through electrical leads running along the catheter from its proximal end. A different approach is described, among others, by Rosen et al. in their U.S. Pat. No. 5,425,735, comprising a catheter with a shielded tip that can be a scraping or an impact element, and an energy source such as a laser with a fiber optic delivery system or a spark generator that creates repeated rapid vapor expansions adjacent the catheter tip. In this manner the vaporizing fluid causes the tip to undergo repeated pulsed movements, thereby enabling it to fracture or cut through an intravascular deposit.
Although the types of devices discussed above have met with varying degrees of success, they all suffer from some common limitations. Erstwhile, guidewires and catheters that transmit vibrating energy from an outside source to an intravascular site quickly lose effectiveness when they are disposed along a tortuous pathway or if they are highly flexible, and most of the vibrating energy is lost in the tissue surrounding the wire. In addition, some of the prior art reports that such guidewires have been known to break when sonic power was applied. Devices that carry the vibration generator at their distal tip for insertion into the patient's body are necessarily limited by the physical constraints imposed by such generators, which must be relatively large to create significant power, and thus preclude any meaningful use in certain applications such as neurovascular intervention. And although physical size is not a constraint with devices such as the Rosen pulsed energy catheter, such devices are relatively expensive, are somewhat difficult to use, and can generate significant heat with the attendant potential for tissue damage.
The acoustic catheter disclosed by Adrian in U.S. Pat. No. 5,569,179 employs a slightly different approach to achieve the same result, namely, generating acoustic energy at the distal tip of the catheter. This catheter is equipped at its distal end with a rotary-to-axial motion converter mechanism comprised of a first magnetic pole pair coupled to the end of a rotary shaft and a second pair of magnetic poles coupled to the proximal end of a non-rotating, reciprocal motion member that slides axially within the catheter. The two pairs of magnetic poles are located in close proximity such that as the first pair of poles is rotated, the second pair of poles is alternatingly attracted and repelled so as to induce reciprocating motion in the sliding member, which in turn generates acoustic energy that is emitted through the distal end of the catheter to ablate matter. This catheter therefore simply utilizes magnetic coupling as parts of its transducer mechanism, and suffers from the same limitations of energy losses due to friction and heat generation in to the surrounding tissue, as well as relative bulk and difficulty of deployment within the vasculature. In addition, this too is a relatively complex, uneconomical device.
Other prior art devices that employ ultrasound to break up thrombi have eliminated the use of an intravascular device completely, relying instead on ultrasounds generated externally of the patient's body and focused upon the target site. U.S. Pat. No. 5,524,620 to Rosenchein, for example, discloses a method whereby ultrasound generators such as piezoelectric crystals or spark type generators produce pulsed or continuous high intensity acoustic energy waves that are focused upon the desired area through what are described as conventional phased-array, time-array techniques. The preferred energy density at the focal area is disclosed to be in the 1 to 20 W/cm2 range, and the acoustic lens is disposed in proximity to the skin of the patient about 5 to 30 cm from the thrombus. While it appears that favorable results have been obtained with this method, it presents the potential for overheating the tissue of the patient disposed between the acoustic lens and the thrombus, as well as the tissue surrounding the thrombus. In addition, the ultrasound generator is specified in the 10 to 50 KW range and produce as much as 100 W/cm2, which is a rather large amount of energy to apply to a living body and would seem to limit the duration of treatment for this method. Reducing the amount of power applied will, of course, result in less energy reaching the target site, thus circumventing the main goal of this procedure.
In light of the above, it becomes apparent that there continues to be a need for a method to induce vibrations within a living body with a simple, efficient device that can be easily disposed within the body, such as an intravascular device that can navigate tortuous vasculature, poses greatly reduced risk of harm to the surrounding body tissue, and can be used for prolonged periods of time.